In an existing long term evolution (LTE) network architecture, if a terminal receives a circuit switched (CS) paging message on an evolved UMTS territorial radio access network (E-UTRAN) network, the terminal needs to return from the E-UTRAN to an UMTS territorial radio access network (UTRAN)/a GSM EDGE radio access network (GERAN) so as to perform the CS service. In this case, an SGs association needs to be established between a mobility management entity (MME) and an MSC for the terminal. An architecture and a processing method for performing the CS service based on the SGs association are referred to as circuit switched fallback (CS fallback, CSFB).
On a conventional mobile communications network, one base station controller (BSC) can only be connected to one mobile switching center (MSC), whereas in an MSC pool networking architecture, one BSC may be connected to multiple MSCs. Compared with conventional networking, the networking has some obvious advantages, such as load sharing, disaster recovery, reduction of inter-MSC location updates, and reduction of inter-MSC handovers.
In the MSC pool architecture, when a terminal is attached to the E-UTRAN and the terminal has called paging in a CS domain, the MSC needs to instruct a corresponding MME to perform CSFB for the terminal to complete the called paging in the CS domain. If a certain MSC in an MSC pool is faulty, its corresponding backup MSC selects a non-faulty MSC to replace the faulty MSC. When the terminal is attached to the E-UTRAN and if the non-faulty MSC cannot find an MME to which the terminal is attached, the non-faulty MSC can only search for the terminal on the GERAN/UTRAN. Therefore, the non-faulty MSC cannot page the terminal, which causes that the called paging is unreachable.